Certain clinical and necropsy findings are described in 53 patients who died from 13 to 185 months (mean 58) after a single aorto-coronary bypass operation. Of the 53 patients, 32 (60%) died from a cardiac cause and of their 73 saphenous vein aorto-coronary conduits 36 (49%) were narrowed at some point more than 75% in cross-sectional area by atherosclerotic plaque; the remaining 21 patients (40%) died from a non-cardiac cause and of their 50 saphenous vein conduits 10 (20%) were narrowed at some point more than 75% in cross-sectional area by plaque. Thus, the non-cardiac mode of death in a large percent of the patients suggests that the bypass operation prolonged life to a degree sufficient for another condition to develop. The 123 saphenous vein conduits were divided into 5-mm segments and a histologic section was prepared from each. Of the 1104 five-mm segments in the 32 patients dying as a consequence of myocardial ischemia, 291 (26%) were narrowed over 75% in cross-sectional area by plaque; in contrast, of the 761 five-mm segments of veins in the 21 patients with a non-cardiac mode of death, 86 (11%) were narrowed over 75% by plaque. Of the total 1865 five-mm segments of vein, only 395 (21%) were narrowed 25% or less in cross-sectional area by plaque. Thus, in patients dying late after coronary bypass the atherosclerotic process continues in all segments of the saphenous veins used as aorto-coronary conduits.